package Others;

import java.util.Scanner;

/**
 * This program will print out the factorial of any non-negative
 * number that you input into it.
 *
 * @author Marcus
 */
public class Factorial {

    /**
     * The main method
     *
     * @param args Command line arguments
     */
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a non-negative integer: ");

        //If user does not enter an Integer, we want program to fail gracefully, letting the user know why it terminated
        try {
            int number = input.nextInt();

            //We keep prompting the user until they enter a positive number
            while (number < 0) {
                System.out.println("Your input must be non-negative. Please enter a positive number: ");
                number = input.nextInt();
            }
            //Display the result
            System.out.println("The factorial of " + number + " will yield: " + factorial(number));

        } catch (Exception e) {
            System.out.println("Error: You did not enter an integer. Program has terminated.");
        }
        input.close();
    }

    /**
     * Recursive Factorial Method
     *
     * @param n The number to factorial
     * @return The factorial of the number
     */
    public static long factorial(int n) {
        if (n == 0 || n == 1) return 1;
        return n * factorial(n - 1);
    }
}
